Determine if an HTML element's content overflows

Normally, you can compare the client[Height|Width] with scroll[Height|Width] in order to detect this... but the values will be the same when overflow is visible. So, a detection routine must account for this:

// Determines if the passed element is overflowing its bounds,
// either vertically or horizontally.
// Will temporarily modify the "overflow" style to detect this
// if necessary.
function checkOverflow(el)
{
   var curOverflow = el.style.overflow;

   if ( !curOverflow || curOverflow === "visible" )
      el.style.overflow = "hidden";

   var isOverflowing = el.clientWidth < el.scrollWidth 
      || el.clientHeight < el.scrollHeight;

   el.style.overflow = curOverflow;

   return isOverflowing;
}

Tested in FF3, FF40.0.2, IE6, Chrome 0.2.149.30.

Try comparing element.scrollHeight / element.scrollWidth to element.offsetHeight / element.offsetWidth

http://developer.mozilla.org/en/DOM/element.offsetWidth
http://developer.mozilla.org/en/DOM/element.offsetHeight
http://developer.mozilla.org/en/DOM/element.scrollWidth
http://developer.mozilla.org/en/DOM/element.scrollHeight

Another way is compare the element width with its parent's width:

function checkOverflow(elem) {
    const elemWidth = elem.getBoundingClientRect().width
    const parentWidth = elem.parentElement.getBoundingClientRect().width

    return elemWidth > parentWidth
}